Elevational decline in soil bacterial diversity and its positive role in driving soil multifunctionality: a global meta-analysis

• Elevation has a negative effect on bacterial diversity. • The regulation of bacterial communities by altitude is essentially climate-driven. • Bacterial diversity enhances the multifunctionality in montane ecosystems. • Climate is the main driving factor in multifunctionality. As a natural variable, the elevation gradient integrates the influences of various environmental factors, these factors and their interactions significantly affect the spatial distribution pattern of soil microorganisms. Global-scale evidence on how elevation regulates bacterial diversity and its subsequent influence on soil multifunctionality remains limited. Here, we collated observational data from 458 global bacterial community along elevation gradients and conducted a meta -analysis to explore the response of bacterial diversity to elevation and the relationships between bacterial diversity and soil multifunctionality. The results demonstrated that bacterial diversity significantly declines with increasing elevation. Climate factors, elevation, total nitrogen (TN), and soil pH had a significant negative impact on the effect size, but soil organic carbon (SOC), available phosphorus (AP), and latitude significantly positive effects, indicating that the regulation of bacterial communities by altitude is primarily climate-driven. Furthermore, bacterial diversity was found to significantly enhance soil multifunctionality in montane ecosystems, with climate emerging as the dominant driver of multifunctionality. Overall, our findings highlight the elevational decline in bacterial diversity and its positive contribution to ecosystem multifunctionality. These insights deepen our understanding of how microbial diversity mediates ecological processes across environmental gradients and provide critical perspectives for predicting ecosystem responses to global climate change.